The Jezero Crater delta, a well-preserved ancient river delta on Mars. New research suggests sedimentary rocks made of compacted mud or clay, like those found in the Jezero Crater delta, are the most likely to contain microbial fossils.
Credit: NASA/JPL-Caltech/MSSS/JHU-APL.

By Corin Campbell

Iron-rich rocks near ancient lake sites on Mars could hold vital clues that show life once existed there, new research suggests. These rocks – which formed in lake beds – are the best place to seek fossil evidence of life from billions of years ago, according to the researchers.

A new review study in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union, sheds light on where fossils of microbes, if they exist, might be preserved on the Red Planet.

In the new study, a team of researchers reviewed studies of fossils on Earth and assessed the results of lab experiments replicating Martian conditions to identify the most promising sites on the planet to explore for traces of ancient life.

The results suggest sedimentary rocks made of compacted mud or clay are the most likely to contain microbial fossils. These rocks are rich in iron and a mineral called silica, which helps preserve fossils. They formed during the Noachian and Hesperian Periods of Martian history between three and four billion years ago. At that time, the planet’s surface was abundant in water, which could have supported life, according to previous research.

The Martian rocks are much better preserved than those of the same age on Earth, according to the researchers. This is because Mars is not subject to plate tectonics – the movement of huge rocky slabs that form the crust of some planets – which over time can destroy rocks and fossils inside them.

The new findings could help inform NASA’s next rover mission to the Red Planet, which will focus on searching for evidence of past life. The U.S. space agency’s Mars 2020 rover will collect rock samples to be returned to Earth for analysis by a future mission.

A similar mission led by the European Space Agency is also planned in coming years.

The new study’s results could aid in the selection of landing sites for both missions. It could also help to identify the best places to gather rock samples, according to the authors.

 “There are many interesting rock and mineral outcrops on Mars where we would like to search for fossils, but since we can’t send rovers to all of them we have tried to prioritize the most promising deposits based on the best available information,” said Sean McMahon, a planetary scientist at the University of Edinburgh in Scotland and lead author of the new study.  

— Corin Campbell is a PR and media manager at the University of Edinburgh. This post originally appeared as a news story on the University of Edinburgh website.